Fuel cell plate flow field

ABSTRACT

A method of manufacturing a fuel cell flow field plate is disclosed in which a generally even flow distribution across the flow field is provided. The method includes providing an inlet manifold in fluid communication with the flow field. The flow field includes multiple channels for which some of the channels receive restricted flow from the inlet manifold as compared to other channels. A relative pressure drop between the channels is altered with a pressure drop feature to encourage fluid flow from the inlet manifold to the channels with restricted flow, which results in a generally even flow distribution across the flow field.

BACKGROUND

This disclosure relates to a fuel cell plate flow field configuration.

A fuel cell includes an anode and a cathode arranged on either side of amembrane electrode assembly. The anode and the cathode are provided by aplate, which includes a flow field. The anode plate flow field deliversfuel to the membrane electrode assembly, and the cathode plate flowfield delivers a reactant to the membrane electrode assembly.

The flow fields are provided by multiple channels that are providedfluid from an inlet manifold. The channels have been arranged in avariety of configurations depending upon a variety of factors, such aspackaging constraints. Typically, it is desirable to provide a manifoldthat is wider than inlets to the channels to ensure a generally evendistribution of flow across the channels. Occasionally, it is notpossible to supply each of the channel inlets with unobstructed flowfrom the inlet manifold. As a result, some of the channels receive asomewhat limited flow, which results in an uneven distribution of flowacross the flow field. Uneven flow distribution can create temperaturegradients across the plate and reduce the efficiency of the chemicalreactions within the fuel cell. In the case of anode flow fields,insufficient hydrogen at a location can create carbon corrosion of theanode plates. In the case of cathode flow fields, insufficient oxygen ata location can cause high temperatures and cell voltage dropoff.

What is needed is a fuel cell plate having a flow field with a generallyeven flow distribution in configurations where it is not possible tosupply an uninhibited flow to at least some of the channels.

SUMMARY

A method of manufacturing a fuel cell plate flow field is disclosed inwhich a generally even flow distribution across the flow field isprovided. The method includes providing an inlet manifold in fluidcommunication with the flow field. The flow field includes multiplechannels for which some of the channels receive restricted flow from theinlet manifold as compared to other channels. A relative pressure dropbetween the channels is altered with a pressure drop feature toencourage fluid flow from the inlet manifold to the channels withrestricted flow, which results in a generally even flow distributionacross the flow field.

In one example, first and second sets of channels are arranged inalternating relationship. Inlet passages from the inlet manifold aremisaligned with the first channels to encourage fluid flow from acrossfirst set of channels in a balanced manner. In another example,unobstructed channels include a shallow channel portion to increase thepressure drop along those channels. Cross-cuts can be used from theunobstructed channels to the obstructed channels to reduce the pressuredrop along the obstructed channels.

What is needed is a fuel cell plate having a flow field with a generallyeven flow distribution in configurations where it is not possible tosupply an uninhibited flow to at least some of the channels.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a highly schematic view of a fuel cell.

FIG. 2 is a plan view of an example fuel cell plate having a flow field.

FIG. 3 is an enlarged view of a portion of the plate shown in FIG. 2.

FIG. 4 is an enlarged view of another portion of the plate shown in FIG.2.

FIG. 5 is a plan view of another example fuel cell plate.

FIG. 6 is an enlarged perspective view of a portion of the fuel cellplate shown in FIG. 5.

DETAILED DESCRIPTION

A fuel cell 10 is shown in a highly schematic fashion in FIG. 1. Thefuel cell 10 includes a membrane electrode assembly 16 arranged betweenan anode 12 and a cathode 14. The membrane electrode assembly 16comprises a proton exchange membrane arranged between gas diffusionlayers, for example. The anode 12 and the cathode 14 respectivelyprovide fuel and reactant flow fields provided by channels in a solid orporous plate. The flow fields are fluidly connected to flow field inletsand exhausts using either internal or external manifolds that are influid communication with their respective fluid flow component.

A plate 18 is illustrated in FIGS. 2-4 having internal inlet and exhaustmanifolds 20, 22. A flow field 24 is fluidly interconnected between theinlet and exhaust manifolds 20, 22. In the example, the inlet andexhaust manifolds are arranged on opposite sides of the plate 18.Parallel channels 26 arranged between risers 28 provide the flow field24. In the example, the channels 26 extend a length L and are parallelwith one another along the length without any significant bends. Thatis, there are no right angle turns and a given channel does not doubleback on itself as is typical with some flow fields. The flow field 24has a width W2 that is greater than the width of the inlet manifold 20.This configuration presents a challenge of evenly distributing fluidacross the flow field 24. Specifically, the channels outboard of theinlet manifold 20 are typically starved of fluid, resulting in an unevenchemical reaction at the proton exchange membrane and hot-cold spots onthe plate 18 or carbon corrosion on the anode side.

In one example, the channels 26 are divided into first and second setsof channels 34, 36 arranged in alternating relationship with one anotherto provide an interdigitated flow field. The first set of channels 34are fluidly interconnected by a lateral inlet passage 32, extending awidth W2, that is supplied fluid from the inlet manifold 20 throughdiscrete, spaced apart inlet passages 30. In the example, the inletpassages 30 are generally evenly spaced laterally from one another andmisaligned with the channels in the first set of channels 34. Thismisalignment encourages even fluid distribution across the first set ofchannels 34. Each channel of the first set of channels 34 extends fromthe lateral inlet passage 32 to a first terminal end 38, best shown inFIG. 4.

Each channel of the second set of channels 36 extend from a secondterminal end 40, which is arranged near the lateral inlet passage 32(best shown in FIG. 3), to a lateral exhaust passage 42 that fluidlyinterconnects the second set of channels 36 with one another. In theexample, there is a pair of lateral exhaust passages 42 interconnectedto and parallel with one another, extending the width W2, as best shownin FIG. 4. The first terminal ends 38 are arranged near the lateralexhaust passages 42. Discrete exhaust passages 44 fluidly connect thelateral exhaust passages 42 to the exhaust manifold 22.

In operation, fluid is supplied to the first set of channels 34 by theinlet manifold 20 via the inlet passages 30. Since the first set ofchannels 34 is dead-ended at the first terminal ends 38, fluid will flowinto the gas diffusion layer of the membrane electrode assembly 16, forexample, and into the second set of channels 36. This interdigitatedarrangement of channels provides a pressure drop feature between thefirst and second sets of channels 34, 36 that evenly distributes flowacross the flow field 24. Fluid from the gas diffusion layer is providedto the proton exchange membrane for chemical reaction. From the secondset of channels 36, fluid is returned to the exhaust manifold 22.

Another plate 118, which has an external inlet manifold 46, is shown inFIG. 5. Fluid is supplied to a header within the plate 118, whichprovides the lateral inlet passage 132, through inlet passages 48. Flowfrom the inlet passages 48 encounters baffles 50 that distribute theflow within the header. The flow field 124 has a width W2 that is widerthan the width of the manifold 46, W1. Flow to the first set of channels134 is generally unobstructed. In the configuration shown in FIG. 5, theflow becomes choked at the extremities within the header at a restrictedflow region 52 such that flow to the second set of channels 136 isobstructed. Risers 128 separate the first and second sets of channels134, 136.

Obstructed flow to the second set of channels 136 would create apressure drop across a length L of the second set of channels 136. Tocounter this pressure drop and provide an even flow distribution acrossthe flow field 124, cross-cuts or cross passages 54 are arranged fromsome of the first set of channels 134 near the header and extending atan angle and away from the header into the second set of channels 136beneath the restricted flow region 52. The cross passages 54 can also bearranged perpendicular to the channels. As a result, flow will be evenlydistributed across the flow field 124 from the inlet manifold 46 to theexhaust manifold through passages 56.

Referring to FIG. 6, another pressure drop feature is shown that can beused instead of or in addition to the cross passages 54 in the plate118. The first set of channels 134, which would otherwise beunobstructed, include shallow channel portions 58 providing a smallercross-sectional area that create a pressure drop across the length L ofthe first set of channels 134. The second set of channels 136 include achannel depth D1 that is greater than the channel depth D2 associatedwith the shallow channel portion 58, which is arranged near the header.The first set of channels 134 may transition from the depth D2 at theshallow channel portion 58 to the depth D1 further downstream. Thelength of the shallow channel portion 58 and its depth are selected toachieve a desired pressure drop that results in an even flowdistribution across the flow field 124. The term “depth” is alsointended to include width.

Although example embodiments have been disclosed, a worker of ordinaryskill in this art would recognize that certain modifications would comewithin the scope of the claims. For that reason, the following claimsshould be studied to determine their true scope and content.

1. A method of manufacturing a fuel cell plate flow field havinggenerally even flow distribution across the flow field, the methodcomprising the steps of: providing an inlet manifold in fluidcommunication with a flow field, the flow field having multiple channelsincluding first and second channels with second channels receivingrestricted fluid flow from the inlet manifold compared to firstchannels; altering the relative pressure drop between the first channelsand the second channels with a pressure drop feature; and encouragingfluid flow from the inlet manifold to the second channels in response tothe pressure drop feature to provide generally even flow distributionbetween the first channels and the second channels.
 2. The methodaccording to claim 1, wherein providing step includes the inlet manifoldhaving a first width and the flow field having a second width greaterthan the first width, and inlets to the flow field arranged across thesecond width.
 3. The method according to claim 2, wherein the providingstep includes the first and second channels extending along a length,the first and second channels parallel with one another along thelength.
 4. The method according to claim 1, wherein the providing stepincludes a lateral inlet passage fluidly interconnecting the firstchannels to one another, the lateral inlet passage fluidlyinterconnected to the inlet manifold by inlet passages, a lateralexhaust passage fluidly interconnecting the second channels to oneanother, the lateral exhaust passage in fluid communication with anexhaust manifold, the pressure drop feature provided by the first andsecond channels being dead-ended by respectively extending from theinlet and exhaust lateral passages to first and second terminal ends,the first and second terminal ends respectively near the exhaust andinlet lateral passages, the first and second channels arranged inalternating relationship with one another.
 5. The method according toclaim 1, wherein the providing step includes a restricted flow area atinlets to the second channels, and the pressure drop feature includes across passage from the first channel near first channel inlets to thesecond channel beneath the restricted flow area.
 6. The method accordingto claim 5, wherein the cross passage extends at an angle relative to alength of the first channels and away from the restricted flow area tothe second channels.
 7. The method according to claim 1, wherein thepressure drop feature includes shallow channel portions in the firstchannels providing a second channel depth that is less than a firstchannel depth of the second channels.
 8. A fuel cell comprising: astructure including a flow field having multiple channels each with aninlet end, and a header in fluid communication with the inlet ends, theheader including a restricted flow region in which fluid flow isrestricted to the inlet ends of a set of channels, and at least some ofthe channels having a pressure drop feature configured to increase fluidflow to the set of channels.
 9. The fuel cell according to claim 8,wherein the pressure drop feature includes a cross passage from firstchannels near first channel inlets to second channels beneath therestricted flow area.
 10. The fuel cell according to claim 9, whereinthe cross passage extends at an angle relative to a length of the firstchannels and away from the restricted flow area to the second channels.11. The fuel cell according to claim 9, comprising an inlet manifoldhaving a first width and the flow field having a second width greaterthan the first width, and inlets to the flow field arranged across thesecond width.
 12. The fuel cell according to claim 11, wherein therestricted flow region is arranged on either side of the flow field atthe inlet ends, the channels extending along a length from the inletheader toward an exhaust header, the channels parallel with one anotheralong the length.
 13. The fuel cell according to claim 8, wherein thepressure drop feature includes shallow channel portions in firstchannels providing a second channel depth that is less than a firstchannel depth of the second channels, the second channels arrangedbeneath the restricted flow area.
 14. A fuel cell comprising: astructure including a flow field having first and second sets ofchannels, each channel of the first set of channels extending from aninlet end to a first terminal end, the inlet ends fluidly interconnectedwith one another by a lateral inlet passage that is configured toreceive fluid from an inlet manifold, each channel of the second set ofchannels extending from an exhaust end to a second terminal end, theexhaust ends fluidly interconnected with one another by an lateralexhaust passage that is configured to provide fluid to an exhaustmanifold, the first and second channels in alternating relationship withone another with the first and second terminal ends arranged near thelateral exhaust and inlet passages, respectively.
 15. The fuel cellaccording to claim 14, wherein the structure includes the inletmanifold, the inlet manifold having a first width and the lateral inletpassage having a second width that is greater than the first width. 16.The fuel cell according to claim 14, wherein the first and second setsof channels extend from their respective lateral passages to theirrespective terminal end along a length, the first and second sets ofchannels parallel with one another along the length.
 17. The fuel cellaccording to claim 14, wherein laterally spaced inlet passages fluidlyinterconnect the inlet manifold and the lateral inlet passage, the inletpassages misaligned with the channels of the first set of channels.